Creation of Magnetic Fields
After reading this section you will be able to do the following:
Define a magnetic field and explain how it is created.
Magnetic Field Creation
A magnetic field describes a volume of space where there is a change in energy. As Ampere suggested, a magnetic field is produced whenever an electrical charge is in motion. The spinning and orbiting of the nucleus of an atom produces a magnetic field as does electrical current
flowing through a wire. The direction of the spin and orbit determine the direction of the magnetic field. The strength of this field is called the magnetic moment.
The motion of an electric charge producing a magnetic field is an essential concept in understanding magnetism. The magnetic moment of an atom can be the result of the electron’s spin, which is the electron orbital motion and a change in the orbital motion of the electrons caused by an applied magnetic field.
Creation of Magnetic Fields
Magnetic Fields
After reading this section you will be able to do the following:
Explain how magnetic lines of flux are affected by other magnetic fields.
In each of the following pictures a magnet is put onto a piece of paper. Then a light dusting of iron filings is sprinkled around the magnet. The lines around the magnets in the following pictures are produced by the iron filings gathering together around the field lines.
Box A
Magnetic field lines run parallel to the magnet until they converge at the poles.
This picture demonstrates what occurs when one magnet is placed on paper, and iron filings are sprinkled around it.
Box B
The magnetic field lines around two north poles bend away from eachother, but still converge at each pole.
Pictured here are two magnets placed on a piece of paper with their like poles facing each other, and iron filings are sprinkled around them.
Box C
The magnetic field lines between a north and south pole connect from one pole to the other instead of circling around to the other end of each magnet.
Lastly, this picture has two magnets placed on a piece of paper with their opposite poles facing each other, and iron filings are sprinkled around them.
What does the pattern made by the iron particles indicate?
You learned in a previous experiment that no matter how many pieces you cut a magnet into, each piece is still a magnet. Even if you shred a magnet into particles the size of sand, each tiny grain is a magnet with a north pole and a south pole. When these magnetized particles are sprinkled over the magnet in Box A, the resulting pattern shows the magnetic field around a single magnet. We can see that the force of the magnet is the strongest at the two ends because more iron particles are concentrated in these areas. The magnetic lines of flux flow from one end to the other.
How do you explain what is occurring?
To understand what is happening, recall from a previous experiment that a magnet allowed to stand freely, like a compass needle, will point to the north in response to the earth’s magnetic field unless it is near a strong magnetic. If the compass is near a strong bar magnet, the opposite poles of the magnets are attracted to each other. We can use this knowledge to identify the magnetic field of a magnet by placing a compass at various locations around the bar magnet and observing where the compass needle points. If the compass is far away from the bar magnet the compass will always point north because it is not in the bar magnet’s magnetic field. As it gets closer to the magnet, the compass begins to point more and more toward the magnet as a result of the force, or the magnetic field, of the magnet. The compass needle aligns itself with the magnetic flux lines of the magnet. Creation of Magnetic Fields
What if…
Let’s say that instead of using one compass to move around the bar magnet, we place thousands of tiny compass needles all around the bar magnet and watch which direction they point and what pattern they make. That is what is happening in our experiment with the iron filings. Each tiny magnetic iron filing is a tiny magnet with a north and south pole, just like a tiny compass. When the iron filings are sprinkled, those very close to the magnet, where the magnetic force is the strongest, will cling to the magnet. Creation of Magnetic Fields
Those filings a little farther away, where the magnetic force is less strong, will align themselves with the magnetic flux lines, but they will not be drawn to cling to the magnet. Those filings even farther away, outside the magnetic force, will point north in response to the earth’s magnetic field. These patterns formed by the direction of the tiny compasses can tell us something about where the magnetic force is the strongest, where it is an attracting force, and where it is a repelling force. In Box B, this pattern indicates a repelling force because the tiny magnets are moving away from the ends of the larger bar magnets. Looking at the pattern in Box C, you see that the two ends of these magnets are attracted because the tiny magnets appear to be lined end to end, attracting to one another and also attracting to the ends of the larger bar magnets. Creation of Magnetic Fields
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